KnowledgeDeliver flaw exploited as a zero-day to install web shells

Hackers exploited a critical zero-day vulnerability in a server running the KnowledgeDeliver learning management system (LMS) to deploy the Godzilla web shell. The flaw is a deserialization issue tracked as CVE-2026-5426 and can be exploited without authentication. It stems from the use of a shared hardcoded machine key in the web portal configuration across all KnowledgeDeliver customer deployments. Threat actors obtained the machine key and used it in ViewState deserialization attacks to sign malicious ViewState payloads and achieve remote code execution at the operating system level. Mandiant in late 2025 responded to an attack on a KnowledgeDeliver server and says that initially, the vulnerability was exploited as a zero-day to inject a malicious script into the web platform. Exploitation was possible due to the use of “identical pre-shared ASP.NET machine keys across multiple customer deployments,” the researchers said. “KnowledgeDeliver installations deployed before Feb. 24, 2026 relied on a standardized web.config file provided by the vendor. This configuration file contained hardcoded machineKey values used by the ASP.NET framework to encrypt and sign data, including ViewState payloads,” Mandiant explains. According to the researchers, the malicious code on the platform “convinced users to download a fake installer,” which led to the machine getting infected with a Cobalt Strike beacon, essentially planting a backdoor. “The payload was encrypted using a key that used...